Abstract : The patent relates to an apparatus which senses an overspeed condition of a high speed shaft, of a turbine for example. There is no wearing moving part unless the shaft overspeeds. Then one pivoted part or arm moves a very small degree carrying a cup-shaped reflector into the path of a small jet of fluid. This reflector cup reflects the jet stream to a receiver hole and conduit. The conduit leads off to apparatus which shuts off the engine or reduces the power input until the shaft speed is reduced below the overspeed limit.